A cerium-based abrasive that achieves a high polishing rate and suppresses the occurrence of surface defects such as scratches and pits and the deposition of the abrasive particles on the polished surface in surface polishing of glass substrates or the like, at low cost with a high production efficiency. The cerium-based abrasive includes a cubic composite rare earth oxide and a composite rare earth oxyfluoride, containing 95.0 to 99.5 mass % of total rare earth elements in terms of oxides, containing 54.5 to 95.0 mass % of cerium in terms of oxide, 4.5 to 45.0 mass % of lanthanum in terms of oxide, and 0.5 to 2.0 mass % of neodymium in terms of oxide relative to the total rare earth elements in terms of oxides, containing 0.5 to 4.0 mass % of fluorine atoms, and containing 0.001 to 0.50 mass % of sodium atoms relative to the total rare earth elements in terms of oxides.

Mixed rare earth carbonate may be prepared by mixing a rare earth sulfate solution with a precipitating agent comprising a first sodium carbonate (Na.sub.2CO.sub.3) solution, to form a first mixture, and generating a higher sulfate rare earth carbonate wet cake from the first mixture. The higher sulfate rare earth carbonate wet cake can be mixed with a second sodium carbonate (Na.sub.2CO.sub.3) solution to form a second mixture, and a lower sulfate rare earth carbonate can be generated from the second mixture.

Mixed rare earth carbonate may be prepared by mixing a rare earth sulfate solution with a precipitating agent comprising a first sodium carbonate (Na.sub.2CO.sub.3) solution, to form a first mixture, and generating a higher sulfate rare earth carbonate wet cake from the first mixture. The higher sulfate rare earth carbonate wet cake can be mixed with a second sodium carbonate (Na.sub.2CO.sub.3) solution to form a second mixture, and a lower sulfate rare earth carbonate can be generated from the second mixture.

A gas sensor capable of detecting carbon dioxide and having high stability is provided. A carbon dioxide gas sensor comprising an insulating substrate 3 and a gas sensing layer 1 formed on one major surface of the insulating substrate 3 via electrodes 2, wherein the gas sensing layer 1 comprises: (a) one or more rare earth metal oxycarbonates represented by Ln.sub.2O.sub.2CO.sub.3, Ln being at least one rare earth metal element selected from Sc, Y, La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Pr, Yb and Lu, the rare earth metal oxycarbonate containing a hexagonal rare earth metal oxycarbonate as a main component; or (b) monoclinic samarium dioxycarbonate,
a production method of the gas sensor, and a method of selectively producing crystal polymorphism of lanthanum dioxycarbonate represented by La.sub.2O.sub.2CO.sub.3 are provided.

A gas sensor capable of detecting carbon dioxide and having high stability is provided. A carbon dioxide gas sensor comprising an insulating substrate 3 and a gas sensing layer 1 formed on one major surface of the insulating substrate 3 via electrodes 2, wherein the gas sensing layer 1 comprises: (a) one or more rare earth metal oxycarbonates represented by Ln.sub.2O.sub.2CO.sub.3, Ln being at least one rare earth metal element selected from Sc, Y, La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Pr, Yb and Lu, the rare earth metal oxycarbonate containing a hexagonal rare earth metal oxycarbonate as a main component; or (b) monoclinic samarium dioxycarbonate,
a production method of the gas sensor, and a method of selectively producing crystal polymorphism of lanthanum dioxycarbonate represented by La.sub.2O.sub.2CO.sub.3 are provided.

A method for producing a solid scandium-containing material comprises providing an aqueous solution containing carbonate ions, carbamate ions, hydrogen carbonate (HCO.sub.3.sup.+) ions, or mixtures thereof, contacting the aqueous solution with a scandium containing material containing one or more impurities to produce a scandium-loaded solution and a depleted scandium containing material, separating the depleted scandium containing material from the scandium loaded solution, treating the scandium loaded solution to cause precipitation of a solid scandium-containing material while avoiding or minimizing precipitation of impurities present in the aqueous solution, and separating the solid scandium-containing material from the solution. In another embodiment, a high purity scandium containing is produced by contacting a solid material containing scandium with an acid to form a scandium loaded solution, separating the scandium loaded solution from any solids, adding additional acid to the scandium loaded solution to reduce the pH and precipitating a high purity scandium oxalate material by adding oxalic acid to the solution.

The disclosure provides, inter alia, formulations comprising cerium (III) carbonate, and processes for producing cerium (III) carbonate. In embodiments, the disclosure provides methods for passivating photodegradation of organic compounds using cerium (III) carbonate.

The disclosure provides, inter alia, formulations comprising cerium (III) carbonate, and processes for producing cerium (III) carbonate. In embodiments, the disclosure provides methods for passivating photodegradation of organic compounds using cerium (III) carbonate.

A gas sensor capable of detecting carbon dioxide and having high stability is provided. A carbon dioxide gas sensor comprising an insulating substrate 3 and a gas sensing layer 1 formed on one major surface of the insulating substrate 3 via electrodes 2, wherein the gas sensing layer 1 comprises: (a) one or more rare earth metal oxycarbonates represented by Ln.sub.2O.sub.2CO.sub.3, Ln being at least one rare earth metal element selected from Sc, Y, La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Pr, Yb and Lu, the rare earth metal oxycarbonate containing a hexagonal rare earth metal oxycarbonate as a main component; or (b) monoclinic samarium dioxycarbonate,
a production method of the gas sensor, and a method of selectively producing crystal polymorphism of lanthanum dioxycarbonate represented by La.sub.2O.sub.2CO.sub.3 are provided.

A gas sensor capable of detecting carbon dioxide and having high stability is provided. A carbon dioxide gas sensor comprising an insulating substrate 3 and a gas sensing layer 1 formed on one major surface of the insulating substrate 3 via electrodes 2, wherein the gas sensing layer 1 comprises: (a) one or more rare earth metal oxycarbonates represented by Ln.sub.2O.sub.2CO.sub.3, Ln being at least one rare earth metal element selected from Sc, Y, La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Pr, Yb and Lu, the rare earth metal oxycarbonate containing a hexagonal rare earth metal oxycarbonate as a main component; or (b) monoclinic samarium dioxycarbonate,
a production method of the gas sensor, and a method of selectively producing crystal polymorphism of lanthanum dioxycarbonate represented by La.sub.2O.sub.2CO.sub.3 are provided.